Valve seat grinding apparatus has been described in U.S. Pat. No. 4,287,688. This patent, which shows a plurality of rotatable satellite grinding wheels attached to a central drive wheel, is specifically incorporated herein by reference.
A problem resulting from reworked valve seats is the reduction of valve sealing ability due to widening of the valve seat surface when the seat is resurfaced. Once the valve seat surface exceeds approximately 55% of the available seating surface of the disk or gate which seats against it, the valve is considered to need replacement. Standard operating procedure for narrowing the width of reconditioned valve seats is to grind a outer angular chamfer around the seat to reduce the annular width with a plate having an annular chamfer cut into the plate. This technique is used only by those highly skilled within the valve reconditioning industry and requires a particular plate for each particular sized valve seat. Such procedure can necessitate the utilization of as many as fifteen plates for different seats within a one valve size diameter.